Combustion furnaces for burning pulverized fuel such as pulverized coal supplied from powder supply devices are known as combustion furnaces used in blast furnace facilities, thermal power plants, and the like. A technique of burning pulverized fuel in such a combustion furnace while spraying the fuel together with air into the combustion furnace is known. Such a burning method using pulverized coal is widely used for such reasons as higher economical efficiency of coal than those of petroleum and LPG (liquefied petroleum gas).
A gas-carried powder supply device that conveys pulverized fuel with carrier gas is known as a powder supply device for supplying pulverized fuel to a combustion furnace. In such a powder supply device, the pulverized fuel in a feed tank is supplied to a powder delivery pipe and conveyed by the carrier gas therein. In general, the supply rate (flow rate) per unit time of the pulverized fuel into the powder delivery pipe is controlled according to the aperture of a powder discharge valve provided at an outlet in a bottom portion of the feed tank and the differential pressure between the pressure in the feed tank and the pressure in the powder delivery pipe (see, for example, Patent Document 1 below).
The flow rate of the pulverized fuel to be supplied into the powder delivery pipe is adjusted on the basis of values detected by a plurality of instruments. Examples of such instruments include a load cell (a weighing scale) that measures the weight of the feed tank. The flow rate of the pulverized fuel to be supplied into the powder delivery pipe is adjusted with a load cell as follows. The weight of powder in the feed tank is obtained by performing tare subtraction, span adjustment, and the like on a load received by the load cell from the feed tank, and the supply rate per unit time of the pulverized fuel supplied into the powder delivery pipe is computed from the rate of change in the weight of the powder obtained by differentiating a change in the powder weight. The aperture of the powder discharge valve and the differential pressure between the pressure in the feed tank and the pressure in the powder delivery pipe are then adjusted on the basis of the computation result to adjust the flow rate of the supplied powder.
From the viewpoint of the adjustment of the flow rate of the supplied powder in this manner, it is important to correctly obtain the weight of the powder in the feed tank from a measurement obtained by a load cell.